Warm Up Objective: Scientists will describe forensic explosives and arson by taking notes and analyzing the activity. What is the topic? What will you be doing? Why is this important? How will you know if you have done well?

Warm Up Objective: Scientists will describe forensic explosives and arson by taking notes and analyzing the activity. What is the topic? Forensic explosives and arson What will you be doing? Notes and activity Why is this important? Evidence; future career choice How will you know if you have done well? Able to describe forensic explosives and arson; completed notes and activity analysis accurately

Fire Investigation Terms Fire - Produced when a substance undergoes rapid oxidation involving heat and light. Fire Triangle – Shows the three elements needed to produce and sustain a fire. Flash Point – The lowest temperature to which a substance must be heated in order for the substance to give off vapors which will burn when exposed to a flame or ignition source. Point of Origin – The location where the fire started. Burn patterns –Noticeable patterns created by the fire as it burns. Accelerants – Substances, such as gasoline, paint thinner, and alcohol, that accelerate the burning process. Arson – A fire started deliberately.

Fuel + Oxygen + Heat = Fire The FIRE TRIANGLE represents the three elements needed for fire to occur: heat, fuel, and oxygen. FUEL OXYGEN HEAT

Fuel can be any combustible material in any state of matter - solid, liquid, or gas.  Most solids and liquids become a vapor or gas before they will burn.  Examples: CLOTHING FURNITURE CURTAINS FLAMMABLE LIQUIDS FUEL OXYGEN HEAT

Fire requires an atmosphere with at least 16% oxygen.  Note: The air we breathe is about 21% oxygen.  FUEL OXYGEN HEAT

Remember: Fuel + Oxygen + Heat = Fire Heat is the energy necessary to increase the temperature of the fuel to a point where sufficient vapors are given off for ignition to occur.  Examples: STOVES HEATING APPLIANCES FIREPLACES DAMAGED WIRING FUEL HEAT OXYGEN

Fire Clues Point of Origin – Burn patterns and other damage can help determine the point of origin, or the location where the fire started. Char Patterns – Created by very hot fires that burn very quickly and move fast along its path, so that there can be sharp lines between what is burned and what isn't. A char pattern on a door would help an investigator determine which side of the door the fire was on. A char pattern on the floor would help investigators determine the use of an accelerant and its path.

Fire Clues V-Patterns - Fire burns up, in a V-shaped pattern, so a fire that starts at an outlet against a wall leaves a char pattern that points to the origin. A very narrow V-shape might indicate a fire that was hotter than normal, such as one helped along by an accelerant. A wide V-shape might indicate a fire that was slow burning. A U-shape could indicate that there was a "pool of origin" rather than a point of origin, such as might be caused by, say, a puddle of gasoline. Heat Shadows - Occur when heavy furniture shields part of a wall; can help determine the origin point.

Fire Clues Glass - Glass fragments, windows, and light bulbs can provide clues to a fire. Light bulbs tend to melt toward the heat source, so the "direction of melt" can indicate the direction of the fire. The shattered or cracked glass of the windows can provide indications as to how a fire burned. A dark soot layer on the glass could indicate a slow, smoldering fire. Clear glass with an abnormal pattern of cracking could imply a very hot fire, possibly due to an accelerant.

Fire Clues Chimney Effect - Since fire burns upwards, there can be a "chimney effect" where the fire ignites at a point, the superheated gases rise upward and form a fireball, which continues straight up to burn a hole in the ceiling. If the roof is not entirely burnt, and the fire investigator finds such a hole, the origin of the fire could be directly underneath. Color of smoke – Determine what type material was burning  Color of flames – Indicates at what temperature the fire was burning.

Image: Havana Rural Fire Department Accident or Arson? Accidental Nature Heating System Electrical appliances Lightning Children playing with matches Smoking Non-Accident Odors – Gas, kerosene, or other accelerants Furnishing – Removal of personal objects and valuables Clothing – Check debris for buttons, zippers, etc Locked windows, blocked doors Two or more points of origin Look for inverted v-patterns (can be a sign that an accelerant was used) Floors charred –Can indicate use of an accelerant Trailers that lead the fire from one place to another Image: Havana Rural Fire Department

Fire Investigation Basics Work from the least damaged areas to the most heavily damaged areas. Document with notes, photographs, and videos. Collect evidence (accelerant samples, fire items, and other crime scene evidence.) Interview witnesses Determine the point of origin. Determine the heat source(s). Hypothesize the reasons for the fire.

Flame Test View the flame test video. How could the flame test results be useful to investigators?

Fire and Materials Burn/put out fires for 8 materials Fabric Printer paper Construction paper Coated cup Plastic Styrofoam Wood Cardboard Observe for time to ignite, fire color, spread speed, duration, results

Analysis Answer the three analysis questions. Which materials are more likely to cause fires to spread quickly? What is your evidence? Which materials would it take a long time for the fire to spread? What is your evidence? How would this data be useful to arson investigators?